1. Field of the Invention.
The present invention relates to thermostable lipogels comprised of a novel aluminum magnesium hydroxy fatty acid compound and organic lipophilic compounds; and to the production of the novel aluminum magnesium hydroxy fatty acid compounds and the thermostable lipogels, as well as to the use of these thermostable lipogels in cosmetic and pharmaceutical preparations.
2. Background of the Related Art.
Gel compositions based on mineral clays which swell, such as montmorrilonites and bentonites, as well as so-called organically-modified bentonites are known; see, for example, Jordan, J. W., Jour. Phys. and Colloid Chem., 53, 294 (1949), or European Patent No. 204,240, which corresponds to U.S. Pat. No. 4,724,098, or Federal Republic of Germany Published Patent Application No. 3,145,449, which corresponds to U.S. Pat. No. 4,434,076, the disclosures of which are herein incorporated by reference.
Bentonites are colloidal, aluminum silicate clays composed chiefly of montmorillonite whose composition in turn is approximately Al.sub.2 O.sub.3.4SiO.sub.2.nH.sub.2 O. The organically-modified mineral clays are known to demonstrate a good swelling effect in oils, fats, and waxes, and form viscous gels in combination with them when formulated with the use of mechanical energy, suitable additives and suitable temperatures.
One great disadvantage of these prior art gel preparations, however, is that they contain very large amounts of substances which can have an irritating effect on skin and which are toxicologically not safe, including polar additives, such as organic polar additives including methanol and acetone, and quaternary ammonium salts introduced by ion exchange. In addition, prior art gel preparations have an inherent brown to beige color which is aesthetically displeasing and, for that reason, disadvantageous if the gel is used in cosmetic formulations.
Federal Republic of Germany Published Patent Application No. 3,732,265 to R. Martin, and co-inventors herein K. Schanz and B. Kaufmann teaches novel aluminum magnesium hydroxy compounds, particularly novel aluminum magnesium hydroxy carboxylates, which have a good swelling effect in oils, fats and waxes. These compounds have the general formula Al.sub.x Mg.sub.y (OH).sub.3x+2y-z R.sub.z.nH.sub.2, in which x=3 to 9, y=4 to 13, z=3 to 5, and 3x+2y=35, and in which R is an aliphatic monocarboxylic acid group having the formula R.sub.1 COO.sup.-, and R.sub.1 COO- contains from 2 to 22 carbon atoms or represents a technical mixture of aliphatic monocarboxylic acid groups containing from 16 to 18 carbon atoms. The compounds function as gellants or gelling agents for certain liquids, in particular, for organic lipophilic compounds which are liquids at 20.degree. C., with which they form gels. The amount of polar additive can be reduced when these compounds are employed to form gels and such gels are useful in cosmetic formulations.
These compounds are distinguishable from the prior art's organically-modified bentonites, however, not only by chemical composition, but also by structure. The structure of these aluminum magnesium hydroxy compounds is a so-called layered structure and is derived from brucite, Mg(OH).sub.2, in which the OH.sup.- ions are characterized by the closest packed hexagonal lattice and octahedral gaps therein are occupied by Mg.sup.+2 cations. The layered structure results from having only every second strata of octahedral gaps occupied by metal atoms.
The replacement of bivalent Mg cations by trivalent aluminum in these aluminum magnesium hydroxy compounds leads to a surplus positive charge in the octahedral gaps which is balanced by aliphatic carboxylates anions in the intermediate layer. In contrast, organically-modified bentonites, which, being layered silicates, have an intermediate layer containing positively charged quaternary ammonium groups to counteract the charge.
These aluminum magnesium hydroxy compounds according to our previous invention, Federal Republic of Germany Published Patent Application No. 3,732,265, form gels in combination with a plurality of organic lipophilic compounds. Moreover, these gels have an absolutely pure white color unlike gels formed with organically-modified bentonites. Such gels are, of course, suitable for cosmetic formulations in which a pure white color is especially important and they contain no quaternary ammonium salts or groups and have a reduced quantity of polar additives. They are, for this reason, less irritating to the skin than corresponding formulations having an organically-modified bentonite base.
The production of gels from these aluminum magnesium hydroxy compounds is, however, not unproblematic, because it requires the use of complicated and expensive mixing assemblies that produce high shear forces, as mentioned in Federal Republic of Germany Published Patent Application No. 3,732,265. Further, the gels produced frequently are not stable enough against temperature effects. In heat stress tests, for example, these gels demonstrate a slight but distinct oil separation at approximately 50.degree. C. The viscosity of the gels changes accordingly and is notably lower, as is the viscosity of cosmetic formulations prepared from the gels. A distinct oil separation is not usually acceptable in cosmetic formulations, however. Moreover, employment of such gels is not economical because the gels should also stablize the finished formulation and, if necessary, additionally, bind any oil therein.
Thus, the inventors continued to seek an improved gel preparation which meets the requirements of (1) substantially no temperature-induced separation of oil, (2) sufficiently high viscosity at elevated storage temperatures on the order of, for example, 50.degree. C., and storability for at least three months, (3) easy reproducibility and economic production, and (4) no content of polar additives or quaternary ammonium salts or groups.